Preparation of lower titanium halides in a molten salt bath



June 28, 1960 R. D. BLUE ETA!- 2,943,033

PREPARATION OF LOWER TITANIUM HALIDES IN A MOLTEN SALT BATH Filed May15, 195'? IN V EN TORS. Robe/'2 0. Blue Marsha/l P. Ale/perv HTTOR/VEVSUnited States Patent PREPARATION OF LOWER TITANIUM HALIDES IN A MOLTENSALT BATH Robert D. Blue and Marshall P. Neipert, Midland, Mich.,assignors to The Dow Chemical Company, Midland, Mich., a corporation ofDelaware Filed May 15, 1957, Ser. No. 659,253

' 5 Claims. (01. 204-64) tion of titanium metal since lower-valencetitanium halides thus dissolved may be electrolyzed in an eflicient andpractical manner to produce metallic titanium and the by-producthalogen, whereas the tetravalent titanium halide cannot be soelectrolyzed. Tetravalent titanium halides, e.g., TiCl cannot beelectrolyzed to produce titanium because they do not ionizesulficientlyto conduct electricity and they cannot be dissolved in molten alkali oralkaline earth halide baths because they are insoluble therein.Furthermore the principal ones which might be so used, e.g., TiCl, andTiBr are unsatisfactory because they volatilize at temperatures too lowto remain in the molten salt bath.

The known lower-valence halides of titanium and particularly thechlorides conduct electricity, are soluble in alkali and alkaline earthmolten salt baths, and do not volatilize at operation temperatures.Therefore, lowervalent titanium halides dissolved in suitable moltensalt baths may be electrolyzed to produce substantially pure titanium.

Titanium is commonly produced by first reducing its ores e.g., brookiteor rutile, as by roasting it with calcium or carbon. The titanium thusproduced is in a relatively impure state, unsatisfactory formetallurgical uses generally. It is commonly then converted to a halide,particularly to the chloride, by chlorination, as by treating withchlorine gas at an elevated temperature. Since titanium is 'tetravalentexcept when limiting'conditions exist, e.g., insuflicient chlorine orinsuflicient time of contact during the chlorination process, thetetrahalide is produced by such reaction. Attempts to control thereaction of titanium sponge or carbon-contaminated titanium with ahalide to produce lower-valence titanium halides have not resulted in asatisfactory product.

The titanium component of the titanium tetrahalide, e.g., tetrachloride,thus produced is thereafter usually reduced to unrefined metallictitanium by reacting the tetrahalide with a metal more electropositivethan the titanium in the electromotive series of elements. Magnesium iscommonly employed although a number of other metals, e.g., sodium,calcium, or lithium, may be also employed. The titanium thus obtained isin the form of a sponge-like mass'which must be especially treated toconvert it to a non-porous compact metal sub stantially free ofimpurities.

Although a trihalide of titanium, e.g., TiCl can be 2,943,033 PatentedJune. 28, 1960 gen gas through a red hot tube, such a method is not ofeconomic importance. Attempts to produce lower-valence titaniumchlorides by passing TiCl vapor into a reactor at an elevatedtemperature containing titanium sponge (which had been produced by thereaction of boiling TiCl, with molten magnesium metal in an atmosphereof helium or argon) have not been successful because the lower-valencetitanium halides form a coating about the particles of titanium andthereby so retard further reaction of the titanium tetrahalides with theinterior of the titanium particle's, even in the presence of a largeexcess TiCl that the method is rendered commercially unfeasible. I

There is, therefore, a need for an improved method of producing lowerhalides of titanium, e.g., TiCl and TiCl in a conducting salt bath, fromimpure sources of titanium including carbides of titanium, from whichductile titanium metal may be recovered by electrolysis of the lowerhalides.

Accordingly it is an object of the invention to provide a novel methodof producing lower-titanium halides dissolved in a salt of a halide orhalides of a metal more electropositive than titanium. i

It is a further object to provide a method of converting impure titaniuminto a form from which substan. tially pure titanium can be subsequentlyrecovered as a ductile non-porous massive metal by electrolysis.

It is a still further object to provide a method of producinglower-valence titanium halides by reacting a halogen-containing reactantwith impure titanium including titanium which contains combined carbon.

The method by which these and other objects are obtained will be madeclear in the following description and drawing.

The drawing is an elevational view largely in section of an apparatususeful in practicing the invention wherein a halogen-containingsubstance in vapor form, e.g., TiCl, or TiBr is passed through a moltensalt bath containing impure titanium metal.

The invention is based on the discovery that unrefined forms of titaniumconsisting of at least titanium, including titanium sponge such as thatproduced by reducing titanium tetrachloride with magnesium, and titaniumobtained by reducing the oxidic forms with carbon, e.g., titanium-carbonalloys or titanium carbides, in molten salt baths, are reactable with ahalogen-containing compound, e.g., HCl, TiCl or Br in vapor'form passedtherethrough, to yield lower-valence titanium halides which dissolve inthe salt bath as they form. As a result, a sufficiently highconcentration of dissolved lower-valence titanium halides are obtainedin the molten salt bath, which are capable'of yielding, on suitableelectrolysis, ductile compact cathode deposits of metallic titanium,leaving the impurities in the salt bath.

The invention then consists of the improved method The salt bathselected should be capable of dissolving the lower titanium halideproduced; be substantially free from contamination by oxygen, nitrogen,or other elements which would have a detrimental efiect on the prod not;be a conductor of electric current; have a comparatively lowmeltingpoint; require a higher decomposition potential than the titaniumhalide produced; be thermally stable at the melting point; andpreferably be substantially non-hygroscopic. Halides of alkali andalkaline earth metals and mixtures thereof may be employed. The alkalihalides generally predominate in the bath since some alkalineearthhalides are hygroscopic. Salt baths Comprising NaCl, K Cl, LiCl,and MgCl and mixtures of any of these salts are usually employed.Particularly satisfactory are the salt baths of NaCl, KCl, or'miXturesof NaCl-KCl and mixtures of LiClMgCl C'aCl approaching the percentagecomposition of the eutectic mixtures.

Referring to the drawing in some detail there is shown an apparatussuitable for practicing the invention and particularly adapted to theuse of TiCl or TiBr as the halogen-containing source. In refractoryfurnace setting 10, having gas burner 11 and flue 12in the wall thereof,is positioned graphite-lined steel pot 14 having removable cover 15thereon. In the bottom portion of pot 14 is transverse plate 16 creatingchamber 17 therebelow. In plate 16 are holes over which there arebaffles 18.

Passing through openings provided therefor in cover 15 are: feed tube 19for particulated solid unrefined titanium metal, vaporous halogen orhalide inlet tube 20 which extends to and opens into chamber 17,vaporous halide or halogen outlet 21, and outlet 22 for molten bathcontaining reaction product. Inert gas line 23 opens into line 20. Valve25 in tube 19, valve 26 in tube 20, valve 27 in tube 21 and valve 28 intube 22 provide a means for controlling flow therethrough. Gas line 24,opening into tube 19, provides a gas, preferably an inert gas, underpressure for forcing thefiuid contents out of pot 14 through line 22when desired. Valves 29 and 30 in gas lines 23; and. 24, respectively,are provided for closing off the respective lines as desired in theoperation of the apparatus, as explained more fully hereinafter.

Reservoir 31 positioned at the top of tube 19 provides a supply ofunrefined titanium particles. Condenser 32 condenses the unreactedvaporous halide leaving pot 14 through tube 21. Line 33 leads to tank 34 where the thus-condensed halide is collected to provide a steadysource of such halide. through line 35: to proportioning pump 36, drivenby motor 37. Vent 38in tank 34 provides an outlet for used inert gas,from the system. Line 39 leads the thus-condensed liquid halide tovaporizer 40. Additional. titanium tetrahalide is fed into vaporizer 40from supply tank 41 through tube 42. The rate of feed through tube 42is, controlled by valve 43. Gas burner 44 provides heat for vaporizingthe halide in vaporizer 40. The thus-vaporized halide passes out ofvaporizer 40 into vaporous halide feed-line 20.

In carrying out the invention, using the apparatus shownin the drawing,an alkali or alkaline earth metal halide or a mixture thereof is placedin graphite-lined steel pot 14 and heated by means of burner 11 to atemperature sufficiently high to melt the salt to form bath 45. Titaniumsponge, titanium-carbon alloys, or other unrefined titanium in the formof pieces 46 is. placed in the bath as by feedingthrough tube 19 fromreservoir 31 by opening valve 25.

Burner 44 is lighted and a titanium tetrahalide, e.g., liquid TiCli 47(or particulated TiBr is placed in reservoir 41 and fed into vaporizer40 through line 42 by opening valve 43 therein. In vaporizer 40 it is.converted to a vapor by the heat from burner 44. An amount of thetetrahalide is fed into vaporizer 46 to maintain a sufficient supply ofboiling titanium tetrahalide therein at a level below the openingsleading therefrom to continuously provide a source of vaporous titaniumtetrahalide. By opening valve 26 in tube 20, the vaporous titaniumtetrahalide from vaporizer 40 passes through tube 20 down into chamber17 in the lower part of pot 14. Valve 27 in line 21 is also opened toprovide complete circulation through reactor pot 14.

When using TiBr or TiCl it is preferable to introduce inert gas underpressure through line 23 by opening valve 29. By passing the inert gas,e.g., helium, through a common line with the vaporous halide-bearingmaterial, the inert gas is saturated with the tetrahalide vapor beforeit enters the reactor. The inert gas thus introduced creates greaterpressure to force the tetrahalide vapor through the bath and aids in theagitation of the bath while the tetrahalide vapor is risingtherethrough. After the titanium tetrahalide vapor enters chamber 17, itpasses upwardly through the openings in plate 16 where it is broken intosmall bubbles and dispersed by baffies 18, and thereafter rises throughbath 45 containing particulate impure titanium 46. Lower-valencetitanium halides, e.g., TiCl and TiCl are formed by the ensuing reactionand are dissolved by the bath. Unreacted titanium tetrahalide passes offthrough tube 21, is condensed in condenser 32 (the temperature thereinnot being sufiiciently low to cause solidification if TiBr is used). Theliquid titanium tetrahalide from condenser 32 drops through line 33 intotank 34 from which it is pumped by pump 36 out through tube 35 and uptube 39 into vaporizer 40. Spent inert gas is vented through vent 33 intank 34.

After the concentration of the lower valence halides has approached thesaturation point in the bath, valves 25, 26, 27 and 29 are closed andthe bath, thus enriched with the lower-valence halides, is removed byopening valve 30 in gas line 24 and valve 28 and tube 22 and introducingcompressed inert gas, e.g., argon, through line 24 which forces theliquid bath and lower-valence halides dissolved therein out through tube22 into a receiver (not shown).

As an alternative mode of practicing the invention, an apparatus may beused in which the impure titanium is placed in a porous or perforatebasket of a conductive material, e.g., of graphite, and placed in aheated reaction vessel, e.g., melting pot 14 containing the moltenhalide salt bath of the invention.

When a halogen-containing substance is employed which exists as a vaporat room temperatures, e.g., Br C1 or HCl, the vaporizer and condenserassembly of the apparatus shown in the drawing may be eliminated and ahalogen source such as a steel tank of the halogenbearing vapor or a.generator of such halogen-bearing substance be'substituted for suchassembly by connecting the outlet of the tank or generator to tube 20and by compressing or by collecting the excess halogen or halide byknown meansv as it leaves the reaction vessel.

. As an alternative mode of removing the bath enriched with thelower-valence halides, a less efiicient but simpler procedure is toemploy an apparatus which is. not equipped with tubes 22 and 24 shown inFig. 1. In such alternative mode, after stopping the reactionsubstantially as above, cover 15 is removed and the enriched molten bathpumped, dipped, or siphoned from the pot into a place of storage ordirectly into an electrolytic cell for electrolysis of the,lower-valance titanium halides therein.

As, a further embodiment of the invention, the pot containing the moltensalt bath and particulate titaniumbearing material may be itself anelectrolytic cell wherein lower-valence titanium halides formed by theintroduetion of a halogen source into the cell according to theinvention may be electrolyzed and titaniummetal recovered from thecathode and the halogen at the anode without transferring the thusenriched bath from the reaction pot prior to the electrolysis.

In the electrolysis of lower-valence titanium halides thus dissolved ina salt bath, whether electrolysis is carried on in a cell which isseparate from the reaction pot or is carried on in the reaction pot,titanium ions move toward the cathode and the halide, e.g., the bromideor chloride ions move toward the anode. The titanium collects at thecathode as substantially pure titanium metal. If the electrolyte pot ismade the anode so that the titanium particles thereby form part of theanode, or if the anode consists of a titanium bar or rod to be consumed,the bromine or chlorine liberated then reacts alkaline halide saltsvaries.

with the titanium particles in the bath or with the titanium bar anodeto form additional lower-valence titanium halides so that little or nobromine or chlorine gas leaves the bath at the anode.

Representative reactions which yield lower-valence titanium halidesWithin a molten salt bath according to the invention are represented bythe following equations in Table I below:

Table I Titanium sponge or titanium alloys containing up to 4% carbonpresent in the reactions represented by the above equations, or someother impure titanium metal present reacts with some of the TiCl thusformed to produce TiCl Ti+2TiCl TiCl The invention is not limited toreactions involving titanium alloys containing not over 4% of the carboncomponent but the presence of TiC, where the carbon component is inexcess of 4%, slows the reaction. and

also results in little reduction of trichloride to the dichloride.

The concentration of Ti and Ti++ in alkali or For example Ti+++, formedupon reacting Ti metal (alloyed with 4% carbon) with HCl gas, reaches aconcentration of 10% at 900 C. in about six hours in a molten KClNaCleutectic bath. Ti+++ formed by reacting titanium sponge with HCl gasreaches a concentration of about 6.25% in about 2 hours at 750 C. in themolten KCl-NaCl eutectic bath. Ti++ concentration is affected by thepresence of Ti+++ ions. For example, the Ti++ concentration reaches 2%in the molten KCl--NaCl eutectic when the Ti concentration is 2.5% butthe concentration of the Ti++ drops 01f to about 1.25% when the Ticoncentration is about 5% and drops below 0.1% when the Ti+++concentration builds up to about 10%. In order that an appreciablepercentage concentration of the divalent titanium ion be reached, it isadvisable to provide an excess of unrefined titanium in the bath andlimit the quantity of the tetrahalide feed so that sufficient titaniumis present to react with the TiCl formed before the percentage of Ti+++has exceeded about 2% which, in terms of TiCl is about 6.4%. V

Table II which follows sets forth the determined concentrations Ti++ andTi+++ as mixed TiCl and TiCl in specified alkali and alkaline earthchloride baths at 900 C.

The rates of reaction of the various reactants contemplated by theinvention vary with the reactants used.

Other conditions, such as state of subdivision and surface condition ofthe impure titanium also affect the rate of reaction but to a relativelyless extent than dothe reactants themselves.

Table III-below shows the relative reaction rates neces sary to form 1gram-atom of Ti+++ for certain reactions when the rate of reaction oftitanium sponge andHCl is arbitrarily taken as 1.0.

Table III Relative Reaction Reaetants Tempera- Rate To ture 0. Form 1gm.-'atom oi T+++ 750 1.0 750 0.25 900 0.53 900 0.10 750 0.03 Ti(4%CH-HBr... 750 0. 17 Tl(4% C)+hellum saturated with T1014 at 124 C 7600.08 'IlC-I-hellum saturated with T1014 at 124 O 820 0.06

The rates of reaction of titanium sponge and HCl vapor according to theinvention are further illustrated by the following example:

900 grams of equimolar TNaCl-KCl eutectic salt mixture were melted in apot to form a bath. Inert gas was supplied in sufficient amount to forma blanket over the bath. The temperature of the bath was maintained atabout 750 C.

TiCl which comprises admixing particulate titanium-.

bearing material containing at least 90 percent titanium selected fromthe class consisting of titanium sponge and titanium-carbon alloyscontaining not more than 4 percent carbon in a molten salt bathselected'from the class consisting of alkali metal and alkaline, earthmetal halides and mixtures thereof, heating said bath to a temperatureof between 750 and 900 C. under'a protective atmosphere of an inert gas,and passing a hydrogen halide gas selected from the class consisting ofHCl and HBr into said molten salt bath at said temperature to contactthe titanium-bearing material therein.

2. The method of "claim 1 wherein the halogen-containingvapor isreleased under pressure'in the bath near the bottom thereof and causedto bubble up through said bath. 3. The method of claim 1 wherein thesalt bath is a mixture of KCl and NaCl.

4. The method of claim 1 wherein the salt bath is NaCl;

5. The method of claim 1 wherein the salt bath is KCl.

ReferencesCited in the file of this patent UNITED STATES PATENTS; I

"/3 grams of M4 inch mesh titanium sponge having a bulk densityofapproximately l were introduced in a graphite, basket immersed in thebath. Dry HCl gas was bubbled through the mixture in excess of the istoichiometric requirement. TiC-l was formed at a rate a

1. THE METHOD OF PRODUCING A MIXTURE OF TICL2 AND TICL3 WHICH COMPRISESADMIXING PARTICULATE TIANIUMBEARING MATERIAL CONTAINING AT LEAST 90PERCENT TITANIUM SELECTED FROM THE CLASS CONSISTING OF TITANIUM SPONGEAND TITANIUM-CARBON ALLOYS CONTAINING NOT MORE THAN 4 PERCENT CARBON INA MOLTEN SALT BATH SELECTED FROM THE CLASS CONSISTING OF ALKALI METALAND ALKALINE EARTH METAL HALIDES AND MIXTURES THEREOF, HEATING SAID BATHTO A TEMPERATURE OF BETWEEN 750* AND 900* C. UNDER A PROTECTIVEATMOSPHERE OF AN INERT GAS, AND PASSING A HYDROGEN HALIDE GAS SELECTEDFROM THE CLASS CONSISTING OF HC1 AND HBR INTO